1. Field of the Invention
The present invention relates to an air conditioner using non-azeotropic mixture refrigerant composed of refrigerant having a high boiling point and refrigerant having a low boiling point.
2. Description of the Related Art
In a heat pump type air conditioner, a compressor, a four-way valve, an outdoor heat exchanger, a pressure-reducing mechanism, an indoor heat exchanger and an accumulator are arranged so as to be successively connected to one another in this order, thereby constructing a loop-like refrigerant circuit. According to this type air conditioner, the refrigerant is circulated through the above parts in the above order under cooling operation by operating the four-way valve, whereby the indoor heat exchanger serves as an evaporator while the outdoor heat exchanger serves as a condenser). On the other hand, the refrigerant is circulated through the above parts in the opposite order to the above order, whereby the indoor heat exchanger serves as a condenser (the outdoor heat exchanger serves as an evaporator).
Recently, from the viewpoint of preventing the destruction of the ozone layer, there has been such a tendency that non-azeotropic mixture refrigerant composed of the mixture of refrigerant having a high boiling point and refrigerant having low boiling point, such as R407C or the like is used as refrigerant for air conditioners. Further, particularly in North America, cooling operation is carried out even in the winter season under which outdoor temperature is low because an air conditioner is put in a computer room or both of a heat source machine and an air conditioner are put side by side in most cases.
When non-azeotropic mixture refrigerant as described above is used, the refrigerant in the evaporator is harder to evaporate as compared with the case where single refrigerant such as R22 or the like is used, and thus the refrigerant pressure in the evaporator is reduced. Therefore, for example when cooling operation is carried out in such an air conditioner under a state where the outside temperature is low, freezing is liable to occur in the indoor heat exchanger. If the freezing is grown, the indoor heat exchanger would be broken, or the evaporation of the refrigerant in the indoor heat exchanger would be insufficient, so that liquid-back to the compressor occurs and thus the compressor is broken. Therefore, in order to avoid the above disadvantage, in the cooling operation under the state that the outdoor temperature is low, the compressor is stopped at the time when occurrence of the freezing in the indoor heat exchanger starts. However, such a control operation to the air conditioner makes it impossible to carry out the cooling operation continuously, so that a stable cooling effect cannot be achieved.
Further, when heating operation is carried out in such an air conditioner as described above, frost is also liable to occur in the outdoor heat exchanger serving as an evaporator even under the cooling operation standard condition of JIS. When frost is liable to occur in the outdoor heat exchanger in the heating operation, the heating, operation must be stopped for a long time to carry out a defrost operation, resulting in reduction in the heating power.
The present invention has been implemented in view of the foregoing situation, and has an object to provide an air conditioner which can suppress occurrence of freezing in an indoor heat exchanger and thus show a stable cooling effect in cooling operation under a state where the outside temperature is low even when non-azeotropic mixture refrigerant is used.
Another object of the present invention is to provide an air conditioner which can suppress occurrence of frost in an Outdoor heat exchanger in heating operation and thus enhance the heating power.
In order to attain the above objects, according to a first aspect of the present invention, an air conditioner including a compressor, a four-way valve, an outdoor heat exchanger, a pressure-reducing mechanism, an indoor heat exchanger and an accumulator which are successively connected to one another to construct a loop-like refrigerant circuit, non-azeotropic mixture refrigerant composed of first refrigerant having a high boiling point and second refrigerant having a low boiling point being filled in the refrigerant circuit and the flow of the non-azeotropic mixture refrigerant being inverted between cooling operation and heating operation by operating the four-way valve, is characterized in that when one of the outdoor heat exchanger and the indoor heat exchanger serves as an evaporator, the first refrigerant of the non-azeotropic mixture refrigerant is stocked in the accumulator while the second refrigerant of the non-azeotropic mixture refrigerant is circulated in the refrigerant circuit, thereby increasing the refrigerant pressure in the evaporator.
According to a second aspect of the present invention, an air conditioner including a compressor, a four-way valve, an outdoor heat exchanger, a pressure-reducing mechanism, an indoor heat exchanger and an accumulator which are successively connected to one another to construct a loop-like refrigerant circuit, non-azeotropic mixture refrigerant composed of first refrigerant having a high boiling point and second refrigerant having a low boiling point being, filled in the refrigerant circuit and the flow of the non-azeotropic mixture refrigerant being inverted between cooling operation and heating operation by operating the four-way valve, is characterized in that in cooling operation under a state where the outside temperature is low, the first refrigerant of the non-azeotropic mixture refrigerant is stocked in the accumulator while the second refrigerant of the non-azeotropic mixture refrigerant is circulated in the refrigerant circuit, thereby increasing the refrigerant pressure in the evaporator.
In the air conditioner of the second aspect of the present invention, the stock of the first refrigerant into the accumulator is performed by increasing the valve opening degree of the pressure-reducing mechanism (expansion valve) when the temperature of the refrigerant flowing in the indoor heat exchanger is equal to a first predetermined temperature or less.
In the air conditioner of the second aspect of the present invention, when the temperature of the refrigerant flow in the indoor heat exchanger is equal to a second predetermined temperature or less, the second predetermined temperature being lower than the first predetermined temperature, the number of revolution of an indoor fan for blowing air to the indoor heat exchanger is increased.
In the air conditioner of the second aspect of the present invention, the number of revolution of an outdoor fan for blowing air to the outdoor heat exchanger is set to any one of plural levels in accordance with the outside temperature.
According to the second aspect of the present invention, in the cooling operation under the state where the outside temperature is low, the first refrigerant (the refrigerant having the high boiling point) of the non-azeotropic mixture refrigerant is stocked in the accumulator, and the second refrigerant (the refrigerant having the low boiling point) of the non-azeotropic mixture refrigerant is circulated in the refrigerant circuit. Therefore, the refrigerant in the indoor heat exchanger serving as the evaporator in the cooling operation is more liable to evaporate, and thus the refrigerant pressure in the indoor heat exchanger is increased. Therefore, occurrence of freezing in the indoor heat exchange r can be suppressed in the cooling operation under the state where the outside temperature is low.
Accordingly, the frequency at which the compressor must be stopped in order to prevent the indoor heat exchanger or the compressor from being broken due to occurrence of the freezing can be remarkably reduced. Therefore, even when the non-azeotropic mixture refrigerant is used, the cooling operation can be continuously carried out under the state where the outdoor temperature is low. As a result, the stable cooling effect can be realized, and an excellent comfortable environment can be achieved.
Further, since the refrigerant having the high boiling point is positively stocked in the accumulator in the cooling operation under the state where the outside temperature is low, there is not required any receiver tank which has been hitherto disposed to avoid the refrigerant from being stocked in the accumulator, and this also enables omission of a pressure-reducing mechanism which has been hitherto required to be disposed in the neighborhood of the outdoor heat exchanger due to the disposition of the receiver tank. As a result the refrigerant circuit can be simplified in construction and the cost thereof can be lowered.
Still further, when the number of revolution of the indoor fan for blowing air to the indoor heat exchanger is increased, the refrigerant flowing in the indoor heat exchanger is more liable to evaporate, so that the refrigerant pressure in the indoor heat exchanger is increased and the refrigerant temperature is increased. As a result, the refrigerant pressure in the indoor heat exchanger serving as the evaporator is increased by circulating the refrigerant having the low boiling point of the non-azeotropic mixture refrigerant, whereby the effect of suppressing occurrence of the freezing in the indoor heat exchanger can be enhanced and thus the occurrence of the freezing in the indoor heat exchanger can be more surely suppressed.
In addition, by stepwise adjusting the number of revolution of the outdoor fan for blowing air to the outdoor heat exchanger in accordance with the outside temperature, the refrigerant in the outdoor heat exchanger serving as the condenser is harder to be condensed, so that the refrigerant pressure in the outdoor heat exchanger is increased and the refrigerant temperature is also increased. This increases the, refrigerant pressure in the indoor heat exchanger serving as the evaporator and also increases the refrigerant temperature, so that the occurrence of the freezing in the indoor heat exchanger can be more surely suppressed.
According to a third aspect of the present invention, an air conditioner including a compressor, a four-way valve, an outdoor heat exchanger, a pressure-reducing mechanism, an indoor heat exchanger and an accumulator which are successively connected to one another to construct a loop-like refrigerant circuit, non-azeotropic mixture refrigerant composed of first refrigerant having a high boiling point and second refrigerant having a low boiling point being filled in the refrigerant circuit and the flow of the non-azeotropic mixture refrigerant being inverted between cooling operation and heating operation by operating the four-way valve, is characterized in that in heating operation, the first refrigerant of the non-azeotropic mixture refrigerant is stocked in the accumulator while the second refrigerant of the non-azeotropic mixture refrigerant is circulated in the refrigerant circuit, thereby increasing the refrigerant pressure in the evaporator.
In the third aspect of the present invention, the stock of the first refrigerant into the accumulator is performed by setting the valve opening degree of an expansion valve serving as the pressure-reducing mechanism on the basis of the room temperature when the heating operation is started and on the basis of a target discharged refrigerant temperature after a predetermined time elapses from the start of the heating operation.
In the third aspect of the present invention, the stock of the first refrigerant into the accumulator on the basis of the room temperature is performed by setting the valve opening degree of the expansion valve to a predetermined fixed opening degree.
In the third aspect of the present invention, the stock of the first refrigerant into the accumulator is performed by setting the valve opening degree of the expansion valve on the basis of the temperature difference between the actual discharged refrigerant temperature of the refrigerant discharged from the compressor and a predetermined target discharged refrigerant temperature so that the temperature difference is equal to zero.
According to the air conditioner of the third aspect of the present invention, under the heating operation, the refrigerant having the high boiling point of the non-azeotropic mixture refrigerant is stocked in the accumulator and the refrigerant having the low boiling point is circulated in the refrigerant circuit, so that the refrigerant in the outdoor heat exchanger serving as the evaporator in the heating operation is more liable to evaporate and thus the refrigerant pressure in the outdoor heat exchanger is increased, thereby suppressing the frost in the outdoor heat exchanger. Therefore, the ratio of the defrost operating time to the heating operation is reduced. Further, since the refrigerant having the low boiling point is circuited in the refrigerant circuit under the heating operation, the refrigerant pressure in the indoor heat exchanger serving as the condenser is increased and thus the heating power of the indoor heat exchanger can be enhanced. As a result, the heating power under the heating operation as the whole air conditioner can be enhanced.
Further, since the refrigerant having the high boiling point is stocked in the accumulator under the heating operation, there is not required any receiver tank which has been hitherto disposed to avoid the refrigerant from being stocked in the accumulator in the refrigerant circuit, and this also enables omission of a pressure-reducing mechanism which has been disposed in the neighborhood of the outdoor heat exchanger because of the disposition of the receiver tank. As a result, the refrigerant circuit can be simplified in construction and the cost thereof can be lowered.
According to a fourth aspect of the present invention, an air conditioner including a, compressor, a four-way valve, an outdoor heat exchanger, a pressure-reducing mechanism, an indoor heat exchanger and an accumulator which are successively connected to one another to construct a loop-like refrigerant circuit, non-azeotropic mixture refrigerant composed of at least one first refrigerant having a high boiling point and at least one second refrigerant having a low boiling point being filled in the refrigerant circuit and the flow of the non-azeotropic mixture refrigerant being inverted between cooling operation and heating operation by operating the four-way valve, is characterized by further including: a controller for controlling the pressure-reducing degree of said pressure-reducing mechanism so that when the heating operation is: carried out or the cooling operation under a low outside temperature is carried out, the first refrigerant of the non-azeotropic mixture refrigerant is stocked in said accumulator and the second refrigerant of the non-azeotropic mixture refrigerant is circulated in said refrigerant circuit, thereby increasing the refrigerant pressure in said evaporator.
According to the air conditioner of the fourth aspect of the present invention, the pressure-reducing degree of said pressure-reducing mechanism is controlled by the controller so that when the heating operation is carried out or the cooling operation under a low outside temperature is carried out, the first refrigerant of the non-azeotropic mixture refrigerant is stocked in said accumulator and the second refrigerant of the non-azeotropic mixture refrigerant is circulated in said refrigerant circuit, thereby increasing the refrigerant pressure in said evaporator. Therefore, the refrigerant in each of the outdoor heat exchanger and the indoor heat exchanger when they serves as the evaporator in the heating operation or in the cooling operation under the low outside temperature state is more liable to evaporate and thus the refrigerant pressure in the evaporator is increased, thereby suppressing the freezing or frost in the evaporator.